S.T.A.L.K.E.R. Clear Sky is the second installment in the underappreciated FPS series developed by GSC Games World. It is important to mention that this review is of the latest, patched version of Clear Sky, version 1.5.04, and not the original retail version. Clear Sky's story is a prologue to the original game, Shadow of Chernobyl, and puts the player in the role of a stalker named Scar. In the beginning, you survive a strange emission that sweeps through the Zone and then begin your journey after being rescued.

The first and most astonishing thing about Clear Sky, as with its predecessor, is how well the mood is established. The design of the game world is practically flawless. There is a great variety of environments that look the part of a post-nuclear torn area. The character models are designed around the idea that people in the Zone are mostly scavengers. The day-to-night cycle makes for a truly immersive experience-the nights are so dark they require a flashlight or night vision gear to get around in effectively.

Aside from the mood it sets, Clear Sky is just a beautiful game to see. Boasting DirectX 10 support and a new host of visual options the player can turn on or off, the game has serious potential and even competes with the likes of Crysis. Every beam of light or casted shadow plays a part in the game's overall look. Dead shrubs and trees, burnt down houses, rustic machinery, and large, open fields and swamps are all brought to life. Moreover, despite the fact that concentration on combat is essential to survival, players will have a difficult time focusing when the environments are this great.

Unlike the original game, which focused on exploration and uncovering the mysteries of the Zone, Clear Sky changes the focus and provides the player with a more combat-oriented game. In Clear Sky, the Zone is relatively "new," and different factions with varying goals and objectives have sprung up and begun fighting for territory and riches. These same factions did play a role in the original game, but the player's ability to interact with them was limited; Clear Sky changes that.

Players now have the chance to ally themselves with different factions as they progress through the story. The overall game world is split into different regions, and each of these regions is, generally, contested between at least two factions. When the player arrives, he is given, at some point, the opportunity to side with a particular faction. Helping one faction defeat another is a simple matter of capturing key locations around the map. These locations could be anything from an old pump station to a road barricade. Once enough objectives are captured and enemies are killed, the balance of power will begin to shift. Then, the player is able to reap benefits from the faction, which could include different types of rewards ranging from new weapons to money to free upgrades.

Unfortunately for the faction wars, once a player effectively eliminates the opposing faction, the struggle ends, leaving you with nothing more than to pick off a few straggling hostiles, bandits, and mutants. And, since certain factions are only present in specific regions of the world, as the player progresses, the opportunity to continue working for one faction ceases. This is a disappointment because it puts a linear taste in an otherwise non-linear game. On the other hand, it does give the player a variety of factions to befriend or fight, but that could have still been an option without the linear feel.

The controls consist of the standard first-person keys and are fully customizable. However, there are a few flaws. For example, there are three types of positions a player can stand in: standing, crouched, and a lower crouch. The issue is that, despite being able to assign a key for each position, you must first be crouched before going into the lower crouch. And, if you want to stand back up to run away, you have to go from lower crouch to crouch before standing. This becomes particularly annoying when in intense fights, since the best way to increase accuracy is to be in the lower crouch stance. There really should be an easier way to move from lower crouch to standing. Aside from minor design flaws, however, the controls are solid and easy to master.

Two of Clear Sky's best features are its A.I. and level of difficulty. Both combined provide enough challenging gameplay to keep even the most veteran FPS gamers on their toes. Don't expect your typical run-and-gun FPS combat where there is no need to find cover, bandage wounds, or upgrade that body armor. Enemies aren't going to just mindlessly run down a corridor while you take pot shots at them. For example, if you're just outside the entrance to a compound, won't be able to camp there and wait for them to just run out. Instead, they'll wait for you to come to them and then jump out from behind an unlikely corner or window. If you're overrunning a position rather easily, hostiles won't just wait for you to continue mowing them down. Not only will they retreat to find better cover, but they'll set it up to try and flank you. There are only a few rare moments when enemies will not have multiple lines of sight on you, which makes it difficult to take them down one by one.